The cellular and molecular basis of the morphogenetic action of juvenile hormone will be studied using the larval epidermis of the tobacco hornworm, Manduca Sexta. This cellular commitment of this epidermis can be changed from larval to pupal by exposure to ecdysone in vitro. Addition of juvenile hormone prevents the change and allows larval cuticle synthesis to begin. The biochemical events which occur in response allows larval cuticle synthesis to begin. The biochemical events which occur in response to ecdysone versus to ecdysone and juvenile hormone will be studied. Also, studies to elucidate the site of action of juvenile hormone in these cells, as well as the metabolism of juvenile hormone by this issue, will be initiated. BIBLIOGRAPHIC REFERENCES: Riddiford, L.M. (1976). Hormonal control of insect epidermal cell commitment in vitro. Nature 259:115-117. Riddiford, L.M. (1976). Mitsui, T. and L.M. Riddiford (1976). Pupal cuticle synthesis by Manduca Sexta epidermis in vitro: patterns of ecdysone sensitivity. Submitted for publication.